A wave impedance inversion method and practical image examples of the medium in the annulus space between the casing and the formation utilizing reflected ultrasonic waves
超声反射法套管-地层环空间介质波阻抗反演方法与成像实例

We propose a wave impedance inversion method of the medium in the annulus space between the casing and the formation utilizing the compound reflected coefficients within the window of resonant transmission frequency of the casing in frequency domain. Calculating formula of wave impedance is obtained by main values of the inverse tangent function of phase_shift at two neighboring frequencies and the corresponding integral character of phase_shift is denoted as the convergent criterion of wave impedance inversion. To solve difficulty of the uncertain acoustic source waveforms and the compound reflected coefficients caused by ultrasonic transducer that is affected by temperature and pressure in downhole casing, the theoretical method of obtaining acoustic source waveforms and compound reflected coefficients from in situ ultrasonic echoes are developed. With processing of synthetic data, the effects on wave impedance inversion results of the medium in the annulus space between the casing and the formation are investigated as the known acoustic and geometrical parameters deviate from the corresponding exact values. The validity of the inversion method is verified by good agreement between the distribution status of the practical medium and wave impedance inversion images after wave impedance images of the data in two scale wells are obtained. Wave impedance inversion and imaging of the medium between the casing and the formation based on the practical data of an oil field are carried out.